The battery decision is one of the most consequential choices in an RV power build, and it’s also one of the most misunderstood. Most comparisons focus on upfront cost. The more useful comparison is about what you get for that money in daily use, over years of cycling.
The usable capacity gap
Both battery types are rated in amp-hours, but that number means something different depending on chemistry.
AGM (Absorbed Glass Mat): To preserve lifespan, AGM should only be discharged to 50% depth of discharge. A 200Ah AGM battery gives you about 100Ah of usable capacity in practice.
LiFePO4 (Lithium Iron Phosphate): Can be safely discharged to 80–90% depth of discharge. A 200Ah LiFePO4 battery gives you 160–180Ah of usable capacity.
That’s a 60–80% difference in usable power from the same rated battery. For everyday RV use, this is the most important number.
→ Size your battery bank based on usable capacity, not rated capacity
Cycle life
| Battery type | Expected cycles (to 80% capacity) | Real-world lifespan |
|---|---|---|
| AGM | 400–600 cycles | 2–4 years with regular use |
| LiFePO4 | 2,000–5,000 cycles | 8–15 years with regular use |
A "cycle" is one full discharge and recharge. If you’re boondocking regularly and cycling your battery daily, AGM wears out fast. LiFePO4 outlasts the RV in many cases.
Weight
A 100Ah AGM battery weighs roughly 60–70 lbs. A 100Ah LiFePO4 battery weighs 25–30 lbs. For a 200Ah system, that’s a 60–80 lb difference, which is significant for payload-sensitive rigs.
Charging behavior
AGM batteries accept charge slowly as they approach full. The last 20% of charge (the "absorption" phase) can take as long as the first 80%. This matters when you’re trying to top off from solar in a limited window.
LiFePO4 accepts charge at full current almost until 100%, then tapers off quickly. In practice, a lithium bank charges 30–50% faster from solar than an equivalent AGM bank. On a partly cloudy day, that speed difference can mean the difference between a full battery and an 80% battery by late afternoon.
→ Calculate how your solar and battery interact for your camping style
Voltage behavior under load
AGM voltage sags significantly under load. When you’re running a microwave or coffee maker from an inverter, the battery voltage drops noticeably, which can trigger low-voltage alarms or inverter shutoffs before the battery is actually depleted.
LiFePO4 maintains a flat voltage curve through most of its discharge range. An inverter running from lithium sees stable voltage and behaves predictably.
Cold temperature performance
Neither chemistry likes cold, but they react differently.
AGM loses capacity in cold and charges slower, but doesn’t require a BMS cold cutoff.
LiFePO4 should not be charged below freezing (32°F / 0°C). Most quality BMS units disable charging at this temperature to prevent lithium plating, which permanently damages cells. Some premium lithium batteries have internal heating pads that allow cold-weather charging; most don’t. If you winter camp in freezing climates, this requires planning.
Cost comparison
A 200Ah AGM bank typically runs $200–$400.
A 200Ah LiFePO4 bank typically runs $600–$1,200 depending on brand.
The lithium premium is real. However, if you replace your AGM bank every 3 years at $300 vs. replacing lithium once every 10+ years at $900, the total cost of ownership is comparable or lower for lithium over a decade.
Which to choose
AGM makes sense if:
- You camp mostly at hookup sites and rarely deep-cycle
- You’re on a tight budget and won’t be heavy users
- You’re in consistently cold climates and don’t want BMS cold cutoff management
LiFePO4 makes sense if:
- You boondock regularly and cycle your battery often
- Weight and payload are concerns
- You want faster solar recharge and more usable capacity
- You’re building a system you don’t want to think about for years
For most serious off-grid RVers, the move to lithium pays off within 2–3 years of active boondocking use.